Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$45.38	11.259%	$50.4893	$50.49	$50.50	$50.50
Purchase #2	$45.51	13.600%	$51.6994	$51.70	$51.70	$51.70
Purchase #3	$24.93	3.639%	$25.8372	$25.84	$25.85	$25.80
Purchase #4	$178.94	6.334%	$190.2741	$190.27	$190.25	$190.30
Purchase #5	$81.98	8.378%	$88.8483	$88.85	$88.85	$88.80
Purchase #6	$24.89	10.308%	$27.4557	$27.46	$27.45	$27.50
Purchase #7	$55.53	8.574%	$60.2911	$60.29	$60.30	$60.30
7 purchase totals =	$457.16		$494.8951	$494.90	$494.90	$494.90